This invention pertains to a method for texturing a magnetic disk and the resulting disk.
It is known in the art to manufacture magnetic disks by the following process:
a) plating a NiP layer on an Al substrate; PA1 b) laser texturing the NiP layer; PA1 c) depositing an underlayer (e.g. Cr) on the NiP layer; and PA1 d) depositing a magnetic layer (e.g. a Co alloy) on the underlayer. PA1 1) NiNb is hard and prevents corrosion. PA1 2) One can form low sombrero bumps in NiNb/NiP. PA1 3) NiNb extends the conditions under which sombreros can be made. For example, on bare NiP, sombreros can only be made using wide spot sizes and low pulse durations. One can form sombreros on NiNb/NiP using small laser spot sizes with longer pulse durations. For example, one can use a 65 ns laser pulse to make sombreros on NiNb/NiP, which cannot be done on bare NiP. 65 ns lasers are common, and well qualified for manufacturing.
Such a process is discussed in U.S. Pat. No. 5,062,021, issued to Ranjan et al., incorporated herein by reference. When one laser textures NiP, under most conditions, one forms a "ridge-shaped" texture feature, e.g. as shown in FIG. 1.
It is possible to form texture features having "sombrero" shapes on NiP, e.g. as shown in FIG. 2, if one uses a wide spot size and a short laser pulse. Such sombreros typically include a central bump 1 surrounded by a depression 2 which in turn is surrounded by a ridge 3. Magnetic disks having sombrero texture features are believed to have better CSS characteristics, i.e. lower friction and stiction between the magnetic disk and a read-write head. ("CSS" means "contact-start-stop", and refers to operation of a magnetic disk drive when it is turned off and then on.) It is desirable to form sombreros having heights less than about 20 nm while ensuring that the ridge 3 surrounding central sombrero bump 1, if any, has a height at least 5 nm less than the height of central bump 1 (and preferably at least 10 nm less than the central bump height).
The reason for keeping the height of central bump 1 below 20 nm is to reduce or eliminate interference between the flying read-write head and the bumps. It is desirable to minimize the flying height of the read-write head with respect to the magnetic film of the disk to maximize magnetic recording performance. The reason for keeping ridge 3 at least 5 nm below the central bump height is to minimize stiction when the read-write head rests on the disk. (The disk typically includes a lubricant layer which can exacerbate stiction. The presence of a high ridge 3 in conjunction with the lubricant can further aggravate stiction.) Furthermore, after many CSS cycles, the top of the bump may exhibit wear. If the clearance between the central bump and the ridge is not sufficient, the effective contact area between the head and the disk would increase rapidly with wear, causing a large increase in stiction.
FIG. 7 shows the relationship between sombrero central bump heights and the iris diameter of a laser used to texture an NiP layer plated on an Al substrate for a selected laser power. (NiP plated Al is a common substrate used in magnetic disks.) Data are shown for laser pulses of 14 ns (curve 5a), 26 ns (curve 6a), 36 ns (curve 7a) and 50 ns (curve 8a). Also shown are the heights of ridges surrounding the sombrero bumps (curves 5b to 8b). As can be seen, there is only a small set of conditions under which one could form a sombrero with a height less than 20 nm, while simultaneously having a ridge height more than 10 nm less than the sombrero height.
FIG. 8 shows the relation between laser power and the sombrero central bump height for laser pulses of 14 ns and a spot size of 10 .mu.m (curve 10), 20 ns pulses and a 10 .mu.m spot size (curve 11), 30 ns pulses and a 11 .mu.m spot size (curve 12), and 36 ns pulses and a 10.5 .mu.m spot size (curve 13). In general, it is often desirable to use a laser power at the curve maximum. See U.S. patent application Ser. No. 08/574,423, filed by Hong Fu, et al., incorporated herein by reference. This is because laser power tends to vary, and it is desirable to avoid sombrero bump height variation caused by laser power variation. This adds a constraint to the texturing conditions which further makes it difficult to achieve a sombrero bump height lower than 20 nm and a ridge height at least 5 or 10 nm lower than the sombrero central bump height.
To summarize, it is difficult to form sombreros having desirable profiles with typical substrates such as NiP plated Al substrates. It would be desirable to be able to form low sombrero bump heights either lacking surrounding ridges, or with very low surrounding ridges.